Automatic train control system



Jan. 26 1937. c, s BUSHNELL 2,068,907

AUTOMATIC TRAIN CONTROL SYSTEM Filed Oct. 5, 1935 2 Sheets-Sheet 1 C 8 1 FIG. 2. u E E 8 51 Normal curren'r" M I2 3 p away cur renT I '2 I I ,F'" o .57MPH\/ nompn INVENTOR C. 5. Bushnell,

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HIS ATTORNEY Jan. 26, 1937. Q s BUSHNELL 2,068,907

AUTOMATIC TRAIN CONTROL SYSTEM Filed Oct. 5, 1935 2 Sheets-Sheet 2 5peed MPH.

. paads; ua/ub 4.1a dO-JP [HM 3 p fi-plaJ UDJUM 4v QaJadwv 11w INVENTOR 6.5. Bushnell,

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Hi5 ATTORNEY Patented Jan. 26, 1937 UNITED STATES PATENT OFFICE Charles S. Bushnell, Rochester, N. Y., assignor to General Railway Signal Company, Rochester,

Application October 5, 1935, Serial No. 43,703

10 Claims.

This invention relates to a train control system of the intermittent inductive type, and more particularly to means for rendering the inductive impulses transmitted at the higher speeds more definitely effective.

The present invention is an improvement which lends itself to being applied to the carcarried apparatus of my prior Patent No. 1,686,434, dated October 2, 1928, although the invention may be applied to other types of carcarried circuits.

In said prior patent a control relay on the car is included in an energizing circuit including the secondary winding of a car-carried inductorium, and a front stick contact of said relay, as well as a source of direct current. In said prior patent, the stick relay (designated GR in the patent) is normally maintained energized by a direct current source, this direct current source being so poled in the circuit that an increase of flux through the secondary coil of the inductorium induces a voltage in this secondary coil which is in opposition to the voltage of said direct current source, so that the stick relay is deenergized due to flux induced in said inductorium. If the flux is increased in the inductorium or receiver due to the passage of the receiver over a stationary track device, it is apparent that the frequency of the voltage induced in the secondary coil is proportional to the speed of the train, and that the time during which such voltage is induced is inversely proportional to the speed of the train. Even though the carcarried stick relay is designed to have a movable soft iron armature of the balanced type that is very light, such for instance, as shown in the prior patent to Leake No. 1,696,170 dated December 18, 1928, the inertia of this armature will nevertheless delay the dropping of the relay in response to the reduction of current flow in the relay due to the induced voltage, especially at the higher train speeds.

In accordance with the present invention, it is proposed to connect a condenser of suitable capacity, across the car-carried stick relay, this in order to increase the bucking current magnetically induced in the winding of the stick relay by the coil of the receiver especially at the higher train speeds.

As an auxiliary feature of the present invention, it is proposed to so connect the condenser in multiple with the car-carried stick relay that open circuiting of the condenser itself will also result in open circuiting of the energizing circuit for the relay which it shunts.

Other objects, purposes, and characteristic features of the present invention will in part be pointed out in the specification hereinafter and will in part be obvious from the accompanying drawings in which:-

Fig. 1 illustrates conventionally a portion only of the car-carried apparatus of a train control system embodying the present invention.

Fig. 2 illustrates graphically the induced voltages and currents in the car-carried relay illustrated in Fig. 1 and the direct current normally flowing in this relay; and

Fig. 3 illustrates by graphs the performance of the apparatus shown in Fig. 1 when condensers of various capacities are connected across the car-carried train control relay.

Description of Fig. 1.--In Fig. 1 has been illustrated the portion of the car-carried apparatus of an intermittent inductive train control system embodying the present invention in which the stick control relay CR may control suitable electro-pneumatic brake control apparatus or brake applying valve EPV in any suitable manner, as conventionally illustrated by the dotted line 2. The precise car-carried circuits may, if desired, be identical to that shown in Fig. 2 of my prior Patent No. 1,686,434, above referred to, to which reference may be had. In the proposed system, the car-carried control relay CR may be of a construction such as illustrated in said prior patent to Leake No. 1,696,170 to which reference may be made for a more detailed description of its construction and mode of operation.

Referring to Fig. 1, this control relay GR is shown included in a stick circuit which may be traced from a suitable car-carried source of direct current, such as the battery BR, through wire 3, front stick contact 4 of the control relay CR, wire 6, secondary coil 8- of the car-carried receiver or inductorium, wire I, one plate 8 of a condenser C, winding 9 of the relay CR, the other plate In of this same condenser C, wire H,back to the other terminal of the battery BR. This control relay CR includes a suitable soft armature 5 of the balanced type, which is pivoted at the middle, as shown, and carries the contact finger 4. This armature 5 is biased to the dotted deenergized position by the spring l2.

It will be noted that the condenser C is connected in multiple with the winding 9 of the control relay CR. This condenser C is provided with two pairs of outlet wires, as illustrated, so that the breaking of one of these outlet wires, or a wire connected thereto will result in the breaking of the direct current circuit traced above. It is, of course, understood that the induction of voltage in the secondary coil S may .produce current in two different circuits, one of which includes the condenser C, and the other of which includes the Winding 9 of the control relay CR. It is well understood by those skilled in the art of railway signalling and automatic train control that it is important that every piece of apparatus of an automatic train control or cab signal system be constructed in accordance with the principle that every failure will be on the side of safety. In accordance with this principle, the condenser C is so connected that the direct current derived from the battery BR must flow through a portion of each of the two plates of the condenser C in order to reach the winding 9 of the relay OR. From this, it is apparent that a complete break down of the condenser C will result in shunting of the relay CR, and that a break in any one of the circuit wires leading to this condenser will result in the opening of the circuit extending to the relay OR.

The secondary coil above mentioned, and designated S in the drawings, is preferably contained on one leg of a soft iron core of a car-carried receiver or inductorium L of general inverted U- shape, the other leg of which is preferably provided with a primary coil P energized by a suitable direct current source such as the battery B. This car-carried receiver L may inductively cooperate with a trackway element T at the entrance to each block of the railroad system. This track element T comprises a U-shape iron core terminating in pole pieces, on the back yoke of which core is contained a bucking coil l5, This coil I5 is normally short circuited through the front contact I6 of a suitable traflic controlling device, such as the line relay LR, so that the coil I5 is open circuited when the line relay LR is deenergized. This line relay LR is controlled in any suitable manner depending upon the type of control desired, but is preferably controlled so as to open its contact l6 when the block at the entrance to which the track element T is located, or the next block in advance thereof, is occupied by a train.

Fig. 2.-Referring to Fig. 2 of the drawings, this figure illustrates graphically the wave form of the voltage induced in the secondary coil S of the car-carried receiver L and the current flowing as a result of this induced voltage. In the curves shown in Fig. 2, voltage and current have been plotted as vertical ordinates and time has been plotted as horizontal ordinates, and the curve E and I show the voltage and current, respectively, for a train moving at assumed speed of, say, 3'7 miles per hour; whereas, the curves E and I show the voltage and current, respectively, for a train moving at, say, 110 miles per hour. The voltages as indicated by the curves E and E are the voltages induced in the secondary coil S due to the change of magnetic flux linking this secondary coil when the car-carried receiver L moves over a track element T with the choke coil I5 of this track element T opencircuited. The current values indicated by the curves I and I are the alternating current components which pass through the winding 9 of the control relay CR when the receiver L passes over a trackway inductor T at speeds of 37 miles per hour and 110 miles per hour, respectively. It will be noted that the voltage waves illustrated by the curves E and E are both of substantially sign wave shape; whereas, the current induced in the circuit including the secondary coil S for these respective voltages comprise only a single wave, as distinguished from the two wave curves E and E These curves very closely approach conditions in actual practice and were obtained from oscillographs taken when testing apparatus such as shown and described in my prior patent above referred to. This result of obtaining a single wave cycle of induced alternating current voltage is due to the fact that it is the initial wave of an alternating current in an inductive circuit, the value of the induced current not returning to zero until the complete cycle of the alternating voltage has been consummated. That is, the second wave of the voltage cycle helps to return the induced current to zero, but is unable to reverse the current in direction.

In the diagram shown in Fig. 2 have been illustrated two horizontal lines in addition to the zero line. The line normal current illustrates the current normally flowing in the winding of the relay CR; whereas, the second line designated drop-away current illustrates the current value at which the relay CR will just drop its armature 5. It will be noted that the alternating current waves I and I are in opposite direction to that of the direct battery current flowing in the winding of the relay CR, so that at any point along the curves I and I this point by its distance above the zero line indicates the actual current flowing in the winding CR, whereas, the distance from this point to the line normal current gives the value of the current flowing in the relay CR by reason of the voltage induced in the secondary coil S.

For convenience, the area within the current curves I and I extending below the line dropaway current has been shown shaded. This has been done to illustrate by shaded lines that portion of time and current that the relay CR is in condition to be dropped away. In this connection, it should be remembered that the mere fact that the current in the relay CR has temporarily dropped below its drop-away value, does not mean that this relay will open its front stick contact 4, this by reason of the mechanical retardation of the relay, due to the inertia of its armature 5. This shaded area shows approximately the duration of time and the extent of current value that the relay current is below its dropaway value, and both of these factors have a bearing on the dropping away of the armature of the relay. Generally speaking, and especially if this shaded area does not extend as low as the zero current line, this area reflects the tendency for the relay to open its stick contact, this by reason of the fact that the extent of the area along a horizontal line reflects time, one of the elements necessary for the relay contacts to open, and the extent of this curve below the line dropaway current is the other element which reflects the dominating effect of the spring [2 over that of the magnetism passing through the armatLu"e 5 of the relay CR. In other words, since the element of time cannot be changed for any given speed it is apparent from these curves that it is necessary to reduce the current in the winding of the relay to as near zero as possible in order to make the shaded area as large as possible, and this is especially true for the higher speed as is very clearly indicated by the shaded areas of the curves I and I and this is what is accomplished by the use of the condenser C connected in multiple with the winding of the relay CR.

Referring again to the voltage and current curves shown in Fig. 2, it will be noted that the alternating voltage cycle E consumes substantially three times as much time as does tr e alternating voltage cycle E It should also be noted that the maximum voltage of the voltage cycle E is substantially three times as high as the maximum voltage of the voltage cycle E Ihis discrepancy in time is, of course, due to the fact that the time during which the car-carried and trackway inductoriums cooperate is inversely proportional to the speed of the train. This ratio of one maximum voltage to the other maximum voltage is, of course, due to the fact that the voltage is directly proportional to the speed of the train. It should, however, be noted that the maximum value of the induced current for these two speeds, as reflected by the curves 1 and 1 is only very slightly different, and this is due to the fact that the circuit of the relay CR and secondary coil is very highly inductive. The inductive reactance of this circuit builds up almost directly in proportion to the frequency of the current, and the voltage builds up directly in proportion to the frequency, so that the induced current is substantially independent or" the frequency or speed of the train. From the foregoing it is apparent that it would be desirable to have the shaded area of the current curves remain as nearly constant as practicable for the various speeds, this in order to have a uniform margin of safety for all of the various train speeds. In this connection it should be borne in mind that the inductive communicating means must not be too sensitive at the lower speeds for otherwise the stick relay CR might be deenergized even though the choke coil i is included in circult for low resistance, as is true when contact I6 is closed. Since the horizontal distances of these shaded areas become shorter as the train speeds become higher, it is apparent that the vertical distances of these shaded areas should become greater as the speed of the train increases. In accordance with the present invention, a condenser C has been connected in multiple with the winding of the relay CR, and it has been found that this condenser C, when of the proper capacity, has the faculty of causing a more pronounced change in current in the winding of the relay CR at the higher train speeds than if no condenser is used. The dotted current line i illustrated in Fig. 2 shows approximately the results obtained at high speeds when a condenser of the proper capacity is used in applicants system.

The exact reason for this effect produced by the condenser C is difiicult to explain. It would, however, seem that the condenser C, which is really in a series alternating current circuit with the secondary winding S, may interact with this secondary winding S to have a resonating effect. Were it not for the relay CR, the condenser C might be chosen to have such a capacity as to cause it to resonate with the inductance of the secondary coil S at a particular frequency, or rain speed. This, however, is not desired because the apparatus is to function at all train speeds, and furthermore, the control relay CR can, of course, not be dispensed with. Also, it is apparent that the condenser C might be of such capacity as to resonate with the inductance of the control relay CR, but if such values of incluctance and capacity were chosen, the units C and CR in combination would result in a unit tuned to potential resonance, so that the impedance of the circuit portion through this unit C-CR would approach infinity at a particular frequency or train speed. Obviously, a structure of this kind would not be desirable because the apparatus is to function at all speeds from as low as /2 mile per hour to 110 miles per hour. In view of the many variable factors involved, such as the inertia of the armature 5, the variable inductance of the relay CR. depending upon the position assumed by the armature 5, the variable inductance of the relay CR due to a variable permeability of the iron included in its magnetic circuit due to variation in current density, and the variations in the inductance of the receiver L, due to the permeability of the iron thereof, depending upon the degree of saturation of the iron, it is virtually impossible to give a theoretical analysis of the functioning of this combination of devices, and accordingly, reference will be made to a chart illustrating the results to be expected by using condensers of various capacities, all as illustrated in Fig. 3 of the drawmgs.

Fig. 3.Referring to the diagram shown in Fig. 3 of the drawings, the vertical ordinates indicate milliamperes at which relay CR will drop at a given speed, meaning the milliamperes of initial battery current in relay CR, and the horizontal ordinates indicate that given speed in miles per hour. It should be noted that although the extreme left-hand portion of this chart reflects zero speed in miles per hour, the extreme bottom portion of this chart does not reflect zero milliamperes, but reflects milliamperes. The horizontal dotted line drawn on the milliamperes line indicates the normal current applied to applicants relay GR in practicing the invention.

Referring again to Fig. 3, and particularly to the horizontal dotted line, it will be noted that when no condenser C is employed, the relay CR will drop under ideal conditions at any speed not above 108 miles. per hour. Since, however, a safety factor should be used, which we will assume is 20 per cent, the apparatus of applicants system with the condenser C omitted would be safe only for train speeds not exceeding five-sixths of 108 miles per hour, which is 90 miles per hour. If now, a condenser of 3.11 microfarads is employed, as indicated by the line 3.11 mfd., the relay CR will operate under ideal conditions for train speeds not exceeding 111 miles per hour. In the same way, if a condenser of 2.11 microfarads is employed as shown by the line 2.11 mfd., the car-carried relay will operate under ideal conditions up to 122 M. P. H. Similarly, if a condenser of 0.55 microfarad is employed as signified by the line 0.55 mfd. the relay CR will drop for any train speed under 123 M. P. H. Similarly, if a condenser of 1.66 mfd. is used, the car relay will operate properly under ideal conditions for all car speeds up to 128 miles per hour. If a condenser of 1.05 microfarads is employed, the car relay CR will drop upon passing over an active (unshorted) trackway device at any car speed between /2 M. P. H. and 140 M. P. H. Applying the factor of safety above mentioned, the apparatus under consideration, when employing a condenser of 1.05 mfd. capacity, would be reliable for all train speeds up to 116 miles per hour.

It has been found by experimental test apparatus that if the condenser capacity is increased to a higher value than any one of those heretofore given that poorer results will be obtained for higher car speeds. For instance, condenser capacities of 3.66, 4.14, 5.19, and 9.94 microfarads includes means for restoring respectively will result in operation of the car relay up to speeds of 104, 103, 98, and 82 miles per hour, respectively, under ideal conditions. It may be pointed out in the case of the last four condenser capacities mentioned, each of which were nounced at the lower train speeds, since each of these last four curves 3.66 mfd., 4.14 mid. and 9.94 mfd. all extend above the remaining curves at car speeds below about 45 M. P. H.

The maximum train speed of 110 M. P. H. heretofore mentioned is a practical consideration, this because locomotives as now used on American railroads do not operate at train speeds higher than 110 M. P. H., and although it is rather unusual that train speeds should even reach this high value, it is necessary for the train control equipment to be constructed to function safely at 110 miles per hour, and since a safety factor of 20 percent is required, the apparatus under laboratory test conditions should function up to 132 miles per hour.

From the foregoing, it would appear that applicants apparatus has certain resonant characteristics such that actual resonance or the maxi mum resonating eifect does not occur until at train speeds much higher than 110 miles per hour, this by reason of the fact that current decrease alone as reflected by the shaded area in Fig. 2 of the drawings, cannot determine the speed at which a relay cannot be relied upon to- 35' operate, this because the time during which current is reduced below the drop-away value is also an important element.

As more fully described, in my prior Patent No. 1,686,434, above referred to, suitable means is provided to prevent the deenergization of the electro-pneumatic valve EPV, and a brake application, if the engineer takes certain precautions and acknowledges his vigilance upon the approach to a point of danger. The apparatus also the control appaan automatic brake application has taken place. It may be briefly stated that in practicing the present invention, the trackway element T is located at the entrance to each block, is so controlled that it constitutes an inert body of iron under caution and danger traific conditions, and that it constitutes such an inert piece of iron containing a choke coil under clear traffic conditions in advance, and that with ratus to normal after the choke coil I5 of the track device T included in a closed circuit of low resistance (which is practically short-circvited) the track device T will not be effective to materially change the flux passing through the car element L upon its passage thereover.

Opc'ration. Let us assume that the car-carried apparatus shown in Fig. 2 passes over the trackway inductor T when the contact B9 of the line relay LR is open. Under this condition, three cycles of alternating current voltage are induced in the secondary coil S. The first and third of these cycles are, however, so insignificant in magnitude that they may be entirely disregarded. The first and third of these cycles is respectively due to the leading pole shoe of the device L bridging the pole shoes of the device T, and the lag ging pole shoe of the device L bridging the pole shoes of the device T, respectively. The middle one of these three cycles of induced voltage is, however, the only cycle of material magnitude and this cycle is induced when the front and rear pole shoes of the car-carried and track elements respectively cooperate, the first wave being induced as these pole shoes approach each other, and the second wave being induced as they recede from each other.

As already pointed out, the current actually induced in the circuit including the relay CR and the secondary coil S in series is of single wave form, this because it is the first material wave of an alternating current flowing in a highly inductive circuit. This current induced by the cycle of alternating voltage, just mentioned, flows through the winding 9 of the control relay CR, and in a direction in opposition to the current flowing therein due to the battery BR, so that the current actually flowing in this Winding 9 at this time falls below the drop-away value for the relay CR, so that its armature 5 begins to open. Dropping of the armature 5, of course, opens the stick contact 4, so that the relay CR cannot again pick up. Dropping of the relay CR will result in the application of the restored to its normal condition manually after the train has been brought to a stop, or after the lapse of a period of time sufficient to bring the train to a stop, all in a manner as more clearly pointed out in my prior Patent No. 1,686,434 and my prior application, Ser. No. 40,329, filed September 12, 1935.

,As already pointed out the factor of safety of at least 20 percent in the margin of operation of applicants system is required, and this factor of safety is necessary by reason of vari ations in various factors having a bearing on the operation of the system. For instance, there are certain variations in battery voltage of the car-carried batteries illustrated in Fig. 1 of the drawings, and forming part of the car-carried equipment, and there are variations in the air gaps between the car-carried receivers on the various cars the various track elements at trackway locations.

Applicant has thus provided a system of automatic train centrol which can be relied upon to inductively transmit an influence from a trackway device to suitable car-carried apparatus at speeds between 1 and 110 miles per hour. For a train moving below one mile per hour an automatic brake application is deemed unnecessary, in that no serious hazard could occur by a train operating at this speed, except at an interlocking point where the engineer is governed by wayside signals, automatic derails and the like.

It may be pointed out that the tests from which the representative curves shown in Fig. 3 have been by test apparatus test apparatus comprised a shaft about which an inductor was rotated so as to pass over a carcarried receiver to leave an air gap such as is used in practice, this inductor having its pole shoes approximately 7%.; feet from the center of the shaft. It is readily apparent that with apparatus of this kind the relative linear speed at which the car-carried receiver and the inductor passed each other could be definitely ascertained by observing the speed of the shaft in question and in taking into consideration the radius at which the inductor was rotated and other obvious factors. It may be pointed out that the reason Why some of the curves in Fig. 3 are not rounded out as smoothly as they might be is due to the fact that insufficient test points were taken in producing the curves.

Having thus shown and described one rather specific embodiment of the present invention, it is desired to be understood that certain variations in the structures employed in practicing the invention may be made without departing from the spirit or scope of the invention, and that the invention may be applied to car-carried systems and circuits other than those shown in my prior patent, all without departing from the invention, except as demanded by the scope of the appended claims.

What I claim. as new is:-

1. In a train control system or" the type described; the combination with a relay having a front contact, a secondary coil contained on a partial magnetic circuit containing a unidirectional magneto-motive force, and source of direct current on a railway car; of a circuit including the winding of said relay, said contact, said secondary coil and said source of direct current in series; an inductorium at a control point along the track for inducing a voltage in said secondary coil upon passage of said partial magnetic circuit by said inductorium; and a condenser connected directly across the winding of said relay.

2. In a train control system of the type described; the combination with a relay having a front contact, a secondary coil and source of direct current on a railway car; of a circuit including the winding of said relay, said contact said secondary coil and said source of direct current in series; an inductorium at a control point along the track for inducing a voltage in said secondary coil upon passage of said secondary coil by said inductorium; and a condenser connected in multiple with the winding of said relay and in series with the source and the secondary coil.

3. In a train control system of the type described; the combination with a relay having a front contact, a secondary coil and source of direct current on a railway car; of a circuit including the winding of said relay, said contact, said secondary coil and said source of direct current in series; an inductorium at a control point along the track for inducing a voltage in said secondary coil upon passage of said secondary coil by said inductorium; and a condenser of the proper capacity connected in multiple with respect to the said secondary coil, with the winding of said relay.

4. In a train control system of the type described; the combination with a relay having a front contact, a secondary coil and source of direct current on a railway car; of a circuit including the winding of said relay, said contact, said secondary coil and said source of direct current in series; an inductorium at a control point along the track for inducing a voltage in said secondary coil upon passage of said secondary coil by said inductorium; and a condenser of a capacity to induce the maximum current in said relay at one hundred and ten miles per hour connected in multiple with the winding of said relay.

5. An automatic train control system comprising, a secondary coil on a railway vehicle; means along the track for inducing momentarily a voltage in said secondary coil as said vehicle passes a control point along the railway track; a car relay having a front contact; a source of direct current on the vehicle; a series circuit including said relay, said contact, said source, and said secondary coil in series; and a condenser connected in multiple with said relay the plates of the condenser being connected to be current conductors in said series circuit.

6. An automatic train control system comprising; a secondary coil on a railway vehicle; means along the track for inducing momentarily a volt. age in said secondary coil as said vehicle passes a control point along the railway track; a car relay having a front contact; a source of direct current on the vehicle; a series circuit including said relay, said contact, said source, and said secondary coil in series; and a condenser of a capacity to induce a large current in said relay at one hundred and ten miles per hour connected in multiple with said relay and having two of its plates connected to be lead-in conductors to the secondary coil.

7. In combination, a relay which if deenergized manifests danger, a normally energized circuit including said relay, and a condenser connected in multiple with said relay to render the relay more readily responsive to a momentary change of the potential energizing said relay, said condenser being so connected that the inlet circuit portion to said relay includes one plate of said condenser and so that the outlet circuit portion includes the other plate of said condenser, whereby said relay is deenergized if said condenser becomes either open-circuited or short-circuited.

8. In combination; a relay; a condenser; and a circuit for energizing said relay which by a wire extends to one plate of said condenser, by a second wire extends from said plate to one terminal of said relay, by a third wire extends from the other terminal of said relay to the other plate of said condenser and by a fourth wire continues on from the other plate of said condenser; whereby short-circuiting of said condenser short circuits said relay and open-circuiting of a condenser lead-in wire results in open-circuiting of said relay.

9. In a train control system of the type de scribed; the combination with a relay having a front contact, a secondary coil contained on a partial magnetic circuit containing a unidirectional magneto-motive force, and source of direct current on a railway car; of a circuit including the winding of said relay, said contact, said secondary coil and said source of direct current in series; an inductorium at a control point along the track for inducing a voltage in said secondary coil upon passage of said partial magnetic circuit over said inductorium; and a condenser connected across the winding of said relay and having such a capacity as to cause the induced voltage in the secondary coil caused by the passage over the inductorium to be greater, than is the case without a condenser, at all speeds from a few miles per hour up to 140 miles per hour.

10. In a train control system of the type described; the combination with a relay having a front contact, a secondary coil contained on a partial magnetic circuit containing a unidirectional magneto-motive force, and source of direct current on a railway car; of a circuit including the winding of said relay, said contact, said secondary coil and said source of direct current in series; an inductorium at a control point along the track for inducing a voltage in said secondary coil upon passage of said partial magnetic circuit over said inductorium; and a condenser connected across the winding of said relay and CHARLES S. BUSHNELL. 

